Westminster city council registrar Alison Cathcart holds a copy of the birth register of Prince George of Cambridge at Westminster Register Office in London August 2, 2013.

Proud papa Prince William has formally registered the birth of his son, Prince George, on a certificate that lists his and his wife Duchess Kate's occupations as "prince" and "princess."

William signed the birth registry on Friday, providing the full name for his son: His Royal Highness Prince George Alexander Louis of Cambridge.

The certificate lists William as the father and "Catherine Elizabeth" as mom. He also provided their occupations as Prince and Princess of the United Kingdom.

When the couple married on April 29, 2011, Kate was formally given the title the Duchess of Cambridge — not princess — by Queen Elizabeth II, even though she was wedding a prince. She was also given the courtesy titles Countess of Strathearn and Baroness Carrickfergus.

But the relationship between "princess" and "duchess" is not always clearly defined, according to Live Science. While a princess technically outranks a duchess, the two titles can overlap. For example, when Sarah Ferguson married Prince Andrew, she became a princess, but because Andrew was Duke of York as well as a prince, she also became Duchess of York.

STEFAN ROUSSEAU / AFP - Getty Images

The birth registration for Prince George lists Duchess Kate's occupation as "Princess of the United Kingdom."